Intercommunication system



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United States Patent 3,130,272 INTERCOMMUNECATION SYSTEM Arie Liberman, Skokie, Ill. Talk-A-Phone Co., 1512 S. Pulaski Road, Chicago, Ill.) Filed Oct. 17, 1958, Ser. No. 767,904 6 Claims. (Cl. 17938) This invention relates to an intercommunication system and, more particularly, to a novel intercommunication system particularly designed for home use.

The system disclosed and claimed herein should be distinguished from the multitude of prior intercornmunication systems which are particularly designed for ofiice or plant operation, as it is intended for home use and incorporates special circuitry and modes of operation which enhance the value of the system for the home over the more conventional systems which have been devised in the past.

One feature of the invention is the provision of a baby sitting mode of operation in which the transducer in one of the stations of the system is switched to a position in which it will only transmit signals to the input of an amplifier, from which they are broadcast to transducers in other stations in the system, and calls directed to the station in the baby sitting condition are blocked. This mode of operation is useful not only for strictly baby sitting applications, but may be used to monitor sick rooms and the like.

Another feature of the invention is a non-private mode of operation in which the transducer of a station is connected to a set of terminals at the station and may be connected through condition selector and station selector switch means in another station with the input or output of an amplifier and the transducer of the other station so that two-way communication may be had with the non-private station, without the necessity for operation of the controls at such station. This mode of operation may, for example, be used in communicating with children in a play area.

A further feature is that the stations of the system are provided with condition selector switch means through which each individual station may be connected for the desired type of operation as outlined above, in addition to normal two-way operation using a talk-listen control.

Yet another feature is the incorporation in the system of a radio receiver to which the various speakers of the system may be connected so that the received radio signals may be broadcast at various points, the circuit having switch means associated with the various condition selector switches of the stations in the power circuit for the radio, so that the operation of any of the condition selector switches to a position for communicating with another station breaks the power circuit of the radio.

A further feature is the provision of a constant impedance speaker circuit including an impedance element connected between the speaker and the output of the amplifier and the second impedance connected in shunt with the speaker and the first impedance, with means for varying the portion of the second impedance shunting the speaker.

Still another feature is the provision of such a system with an auxiliary radio and amplifier in an additional station of the system, with circuitry including an impedance network for attenuating incoming signals to the second station so that they are not excessively amplified by the dual amplifier system.

Yet a further feature is the provision of safety circuitry in the system, including a diode in the power circult to prevent application of improper voltage polarities to the transistors of the amplifier. A heat-sink is associated with the power transistors in the amplifier circuitry to dissipate heat, reducing the chance of damage to the transistors from excessive currents.

And another feature is the provision of a balanced coupling element, including a doubled conductor wound in a coil, having a tap at the center of the conductor dividing the conductor into two equal coil portions, and means connecting the two portions of the conductor in series and in additive phase relation, the connecting means establishing an accurate center tap of the coil.

Further features and advantages will readily be apparent from the following specification and from the drawings, in which:

FIGURE 1 is a block diagram of a representative intercommunication system embodying the invention;

FIGURE 2 is a circuit diagram, partially in block and partially in schematic form, of a portion of the intercornmunication system, including the power circuitry;

FIGURE 3 is a schematic diagram of the control circuits of a station of the system;

FIGURE 4 is a schematic diagram of a modified control circuit arrangement of a station of the system;

FIGURE 5 is a schematic diagram of an outdoor substation;

FIGURE 6 is a schematic diagram of an indoor substation;

FIGURE 7 is a fragmentary circuit diagram illustrating the radio power circuits;

FIGURE 8 is a perspective view of a transistor mounting embodying the invention;

FIGURE 9A is a schematic diagram of a coupling transformer; and

FIGURE 9B is a diagrammatic illustration of the coupling transformer of FIGURE 9A.

The home intercomrnunication system disclosed and claimed herein incorporates several types of stations and Various modes of operation. A representative system will be described in detail and related to various household functions. It will be understood that many modifications of the system may be made, as dictated by the layout of the home and the nature of the family it is to serve.

Referring now to FIGURE 1 of the drawings, an intercommunication system is shown including a master sta tion 15, two staff stations 16 and 17, an indoor substation 18 and an outdoor substation 19. The stations are also indicated by system numbers 1, 2, 3, 4 and 5 respectively. The system is energized from a suitable power source 20. The stations are interconnected by cables, as is Well known in the art.

In a typical home, the master station 15 might be located in the kitchen, in a family room, or in a oentrally located hallway, for example, depending on the most convenient spot for the primary system controls. Incorporated in the master station, as will appear more fully below, are a radio receiver and the amplifier circuits for the system, in addition to the condition and station selector switch means. The staff stations 16 and 17 are similar to the master station in that they include condition and station selector circuitry; but they do not include a radio receiver ar amplifier circuits. Staif stations may advantageously be located in the laundry room, playroom, certain bedrooms, den, workship, or the like.

The indoor substation 18 is a unit which may receive and answer calls and which can be used for baby sitting or monitoring purposes. The station cannot originate calls directed to a particular other station of the system.

Units such as this are often located in a nursery, work shop, or other location where monitor service is desired and from which it is not necessary to originate calls. The outdoor substation 19 is intended for use at the doors of the house and includes circuitry for permitting a caller at the door to carry on a conversation with someone within the house under the control of the person within the house.

FIGURE 3 illustrates the common circuitry found in master and staff stations. A multiple section conditionselector switch means 22 has seven sections designated by the letters A, B, C, D, E, F and G on the drawing, and which will be referred to by the reference numeral and letter in the following discussion. The selector switch means 22 has five positions which may be designated (clockwise from the top-most position) baby-sit, non-private or neutral, private, listen and talk. The positions of the condition selector switch will be referred to below as B, N, P, L and T, respectively.

Each of the master and staff stations of the system is provided with a terminal board as illustrated in FIG- URE 3, having pairs of terminals for connection with the cables between the units, there being a set of numbered terminals, with numbers coresponding to the various stations. of the system, and here shown as 1-8. The pair of terminals designated XX will be described below. The terminals RR and TT are connected to the input and output of the system amplifier, respectively;

The station selector switch means 24 have sections connected with the numbered cable terminals and to a secondary terminal board 25. By means of the secondary terminal board and interconnection between the station selector switches shown in FIGURE 3, the station may be connected for private or non-private operation with respect to the other stations. A connection between the numbered station terminals on the terminal board 25 and the lettered terminals MM establishes private operation, while a connection with 8-8 provides non-private operation. Further details of this circuit may be found in Liberman Patent 2,658,947. a

The additional circuitry (beyond that of a staff station) provided in the master station is illustrated in FIG- URE 2, which in part parallels the showing of FIG- URE 3 in the inclusion of terminals R-R and TT. The master station includes both a radio receiver 26, amplifier 27 and power amplifier 28, all of which are preferably made up of transistor receiving and amplifying circuits. The radio receiver portion of the circuitry may be omitted if desired.

In addition to. the connections between the amplifier input, and terminals RR, and the amplifier output and terminals TT, FIGURE 2 illustrates the power circuit for the system in which a power source, as battery 29 is connected to the terminals indicated plus and minus, with the minus terminal being grounded. Connected between thepower terminals and the amplifier 2728 are a fuse 30 and a diode 31. A series droppingresistor 32 provides reduced voltage for a portion of the amplifier circuitry and for the radio circuits which are connected into the power circuit through conductors 33, to terminal; B, and 34, connected with terminal E.

As the amplifiers and radio preferably utilize transistor amplifying elements, it is essential that precautions be taken to prevent the householder from inadvertently connecting the power source into the system with the improper polarity, as this wouldburn out at least some of the transistors. Accordingly, diode 31 is placed in the power connection to the positive (plus) terminal, with a polarity such that current can flow only in the proper direction. The fuse 30 preferably has a fast blow characteristic, breaking the power circuit quickly in the event of an overload. As a further safety feature, a heat-sink, as fuse clip 32, FIGURE 8, which has a relative high mass is mounted on power transistor 33 of '4 the amplifier circuit and serves to aid in the dissipation of heat from the transistor, preventing damage upon intermittent surges of high current drain in the circuits, as with noise impulses in the signals being amplified.

In order to consider adequately the operation of the condition selector switch means 22, it is desirable first to summarize the cable arrangement interconnecting the various stations of the system. Each of the stations is assigned a number, as the numbers 1, 2, 3, 4 and 5 shown in FIGURE 1. Suitable multi-conductor cable pairs are strung between the stations and a number assigned to each pair, which pair is then connected to the appropriate terminals of the stations, including the lettered terminals R-R, TT and 13-0. The cable pair having the number corresponding with the number of the station is then removed from the numbered terminals and connected with terminals XX. In the master and staff stations, desired connections are also made between the numbered terminals on secondary terminal strip 25 and terminals MM or 8-8, depending upon the type of operation desired.

The master and statf stations each include a two-way transducer or speaker-microphone 35 connected in series with a resistor 36, the series combination being shunted by a potentiometer 37. The movable tap of potentiometer 37 is connected with the juncture between resistor 36 and speaker 35. The series resistor 36 preferably has an impedance of the same order as the impedance of the voice coil of speaker 35, while the shunting resistor is several times larger. For example, in a circuit using a transducer having, a 13 ohm voice coil, resistor 36 has a value of 15 ohms and potentiometer 37, ohms. As the position of the movable tap of potentiometer 37 is varied, the volume for loud speaker 35 is likewise varied, while the total impedance of the circuit remains substantially the same, as it is determined essentially by the resistance of a series combination of the speaker and resistor 36. This arrangement precludes a reaction on the power amplifier circuits when the volume of any individual station is varied.

Turning now to a detailed consideration of the circuitry of FIGURE 3, each of the conditions of operation of the unit will be considered. When condition selector switch 22 is in the talk or T position, the transducer 35 is connected through sections 22A and 22B of the switch to terminals R-R, the input of amplifier 27. The output of the amplifier, which appears at terminals TT, is coupled directly to the transducer of any station in the system which is in the private or listen position, as will appear, and through sections 22C, 22D, 22E and 22F of the condition selector switch of the call originating station to the station selector switch means 24. The need for four sections of the condition selector switch to accomplish this operation is dictated by the. private"-non-private coupling arrangement provided by the auxiliray terminal strip 25 and the associated terminals, aswill appear from a consideration of the circuit of FIGURE 3. Thus, if the operator of the call originating station has closed one of the station selector switches, the call passes from the amplifier output terminals through the selector circuitry to the proper cable pair for, the station which is to receive a call. Such calls are received at the other station on terminals XX, and are coupled directly to the called station transducer through the selector switch sections A and B, if the call receiving station is in the non-private or N position.

In the listen or L position of selector switch 22, transducer. 35 is connected through switch sections 22A and 22B directly with the amplifier output terminals TT. At the same time, connections are made through the station selector switches for those stations connected with terminals S-S (non-private operation) and condition selector switch sections 22C and 22D to amplifier input terminals R-R. If the particular station with which a conversation is being had is connected for private operation with respect to the call originating station (terminals M-M), the other station must operate its condition selector switch to the talk position in order to answer. This prevents monitoring conversations at such other station where privacy is desired.

In the private or P position of the condition selector switch 22, the transducer or speaker 35 is again connected with amplifier output terminals 22. In the nonprivate or N position, the transducer is connected with terminals X-X, and can receive and answer calls only when connected with the amplifier through the station selector circuitry at another station.

In the baby-sit or B position of selector switch 22, transducer 35 is connected directly with amplifier input terminals RR, and incoming calls directed to that station are blocked in sections 22A and 22B of the selector switch. Thus, no action taken at another station can cause a signal to appear at the speaker of a station in the baby-sit position. This makes the baby-sit mode of operation extremely desirable for monitoring not only a nursery, but a sick room or the like where it is important that other stations be able to hear what occurs at the monitored station, but no disturbance at the monitored station is permitted.

It will be noted that in the private position, the station is able to listen to all signals appearing in the output of the amplifier, but originates no signals itself. A station in this condition may be called by another station by merely pressing the control switch at the other station to the talk position, and it is not necessary that the calling station utilize its station selector switches. In the non-private position, the transducer 35 is connected with the amplifier only through the circuitry of another station, so that it is necessary for the other station to select the station in the non-private condition before a conversation may be carried on. This arrangement is particularly useful in communicating with a childrens play area, as the user of another station may select the non-private stations number on the station selector switch and, with the condition selector switch in the listen position monitor the situation in the play area. A two-way conversation may be carried on with the station in the non-private condition with only the other party to the conversation operating the condition selector switch 22 between the listen and talk positions. This arrangement is also useful in a shop or laundry area or other place where the called person may not conveniently operate the talk-listen switch of the called station.

Returning to a consideration of FIGURE 2, it will be seen that the output of transistor radio 26 is connected with amplifier 27 and through power amplifier 28 to the output terminals TT. Thus, when the radio is in operation, which is determined by the setting of controls at the master station where the radio is located, the program being received is available at terminals TT throughout the system. Thus, any station which wishes to listen to the radio may do so by operating its condition selector switch 22 to a position connecting the transducer 35 with the amplifier output. As seen in FIG- URE 3, the transducer is so connected when in either the private or listen positions. However, in order to avoid having the radio interfere with conversations between stations, the radio power circuit, conductors 33 and 34 connected with terminals E and B includes section 226 of the condition selector switch and is complete only when all of the stations of the system are in the baby-sit, non-private or private positions. This is best seen in FIGURE 7 where the station 15, in which the radio receiver is located, has one terminal of the radio power circuit attached to the B terminal and connected through a cable with the G section of the condition selector switches at stafi stations 16 and 17, through connections to terminals B and O at each of these stations. The circuit returns to the master station 15, on

the 0 terminal, from which a connection is made through section G of the condition selector switch to terminal E, to which is connected the radio circuitry 26. Thus, whenever any condition selector switch in the system is operated to the talk or listen positions, the radio is rendered inoperative. Of course, although the radio power circuit is completed through the condition selector switch or" a station in the baby-sit or non-private condition, the output of the radio is not coupled to these stations, as the transducer is not connected with the output terminals TT of the amplifier.

FIGURE 5 illustrates the circuitry of an outdoor substation, indicated at 19 in FIGURE 1. The sound circuitry includes merely a transducer 40 connected through the series resistor 41 to a pair of terminals, to which the appropriate numbered cable for the outdoor substation (here number 5) is connected. The additional circuitry for the outdoor substation is associated with a doorbell or chimes. A step-down transformer 42 is energized from the volt A.C. line and has connected to its secondary winding an operating coil 43 for the doorbell. Connected in series with doorbell 43 is a light bulb 44, which may be used to illuminate a nameplate on the outdoor substation housing. The impedance of the light bulb 44 is such that insufiicient current flows in the circuit to actuate the doorbell 43. Connected in parallel with light bulb 44 is a switch 45, also located at the outdoor substation, and which when closed shorts across the light bulb, connecting doonbell 43 directly across the secondary winding of transformer 42. When this occurs, the increased current in the circuit actuates the doorbell. Upon operation of the doorbell, som one inside the house may step to the nearest master or staff station of the intercommunication system and press the station selector switch for the outdoor substation. Then, by manipulation of the talk-listen switch, a two-way conversation may be conducted with the person at the door.

Circuitry for an indoor substation 18 (station number 4) is shown in FIGURE 6. The indoor substation is provided with three pairs of terminals RR, TT and a numbered pair corresponding with the number of the station. The transducer 59 is connected through a volume control circuit 51 with the movable contacts of a double-pole, double-throw switch 52. In the B position of the switch, the transducer is connected directly to the terminals RR, the amplifier input. This provides the baby-sitting operation, in which the transducer 59 operates strictly as a monitor, and no calls can be received at the substation.

In the other position of switch 52, designated K, the transducer is connected to the switch 52 with the movable contacts of a second double-pole, double-throw switch 53, the N position of switch 53, in which the contacts are shown, correspond with the N, or nonprivate condition of staff or master station, with the transducer connected to the numbered terminals so that calls may be directed to the substation from a master or stafi station, and the substation can answer without manipulation of the switches. In the P position, the circuit corresponds with that of the P or private position of the master or stafi station, the transducer being connected to the terminals TT, the output of the amplifier. In this condition, the substation may listen to the radio if it is operating and can hear any calls on the system.

in the event it is desired to provide additional radio receivers in the system, so that a station other than the master station can select its own radio programs, the modified circuitry of FIGURE 4 is provided in a station which may be referred to as an additional master. The station selector circuitry has been omitted for clarity. The condition selector switch for the additional master station, here designated 56, includes additional sections 7 H, I and I. The principal difierence in this circuitry is in the connection of the elements in the P or private position of the selector switch. It will be recalled that in a master or in a stafi station (FIGURE 3), when the circuits are in the P position, the transducer 35 is connected directly to the amplifier output terminals T-T. In the additional master circuitry of FIGURE 4, in the P position, the transducer is connected to the output of internal amplifier 57, associated with radio receiver 58. If with the additional master in the P position, a call is directed to the additional master station from another station in the system, the amplifier incoming signal appears at terminals XX and is connected through sections I and I of selector switch 56 through an attenuator network 59 and from the attenuator to amplifier 57 and thus to the transducer 60. This circuitry prevents overloading the transducer 60 which might occur if the incoming signals were reamplified without attenuation. In order that the additional master station may answer such a call, it is necessary to move the condition selector switch 56 to either the N or the T position.

The power circuit for the radio 58 and amplifier 57 is completed through section H of condition selector switch 56, which is closed only in the private position, so that the radio and amplifier are rendered operative only in this single condition of the circuit. The babysit, non private, listen and talk circuitry is identical with that of FIGURE 3 and Will not be described again.

'In an intercomrnunication system with many cables extending between the various stations, interference from outside sources is an extremely serious problem. In the system illustrated, novel balanced cable termination circuitry is provided at the input and output of the amplifier circuits of the master station. As shown in FIGURE 9A, this special circuitry takes the form of a balanced coupling transformer 65 having winding 65a, to which the cable is attached, center tapped and grounded. Here the .ground is indicated as a connection from the center tap of the winding to the core 65b of the transformer and through the core to ground 66. The winding 65a is the primary winding of the amplifier input transformer and the secondary winding of the amplifier output transformer. A novel arrangement for achieving an accurately balanced center tapped transformer winding is illustrated in FIGURE 9B. The coil 65a is wound from a doubled conductor forming a pair of interwoven coil portions 67 and 68 which are exactly equal in the number of turns, resistance and inductance. The doubled end of the coiled conductor, as the lower end, is broken and a connection 69 made between the lower end of coil 67 and the upper end of coil 68. This connects the two coils in series and in additive phase relation. As the two coil portions are equal in number of turns, resistance and inductance, a connection to conductor 69 provides: an extremely accurate center tap. It has been found that an accurately tapped coupling element of this type substantially completely eliminates induced interference on the cables of an intercommunication system.

While I have shown and described certain embodiments of my invention, it is to be understood that it is capable of many modifications. Changes therefore, in the construction and arrangement may be made without departing from the spirit and scope of the invention as disclosed in the appended claims.

I claim:

1. In an intercommunication system: a plurality of stations; an amplifier in said system having an input and output; a two-way transducer in each station; station selector switch means in a first of said stations controlling interconnection of said first station with a selected other station; condition selector switch means in said first station actuable to control connection of the transducers in said first and said selected other stations with the input and output of said amplifier to carry on a two-way conversation; a first terminal in said other station connected directly with the output of said amplifier; a second terminal in said other station connected with the station selector switch means of said first station; and switch means in said other station connected with the transducer therein and operable to connect said transducer with one or the other of said terminals.

2. The intercommunication system of claim 1 in which said other station includes a third terminal connected with the input of said amplifier, and the switch means in said other station having a position connecting the transducer therein with said third terminal.

3. -In an intercommunication system: an amplifier having an input and an output; a plurality of stations in said system, each having a two-way transducer; cable means interconnecting said other stations with the called station terminals of said call originating station; station selector switch means in at least one of said stations; called station terminals in each station with a station selector switch, said switch being operable to effect an interconnection between the call originating station and a called station terminal in said call originating station; condition selector switch means in the call originating station, selectvely actuable between talk and listen positions to connect the transducers selectively with the input or output of said amplifier; first terminals in said call receiving station con nected with the output of said amplifier; second terminals in said call receiving station connected with the called station terminals of the call originating station; a condition selector switch in said call receiving station having private and non-private positions and selectively actuable therebetween, connecting the transducer of the call receiving station with said first terminals and the amplifier output in the private position and with the second terminals in the nonaprivate position.

4. In an intercommunication system: a master station; an amplifier in said master station having an input and an output; a speaker in said master station connected with theoutput of said amplifier; at least one additional station connected with said master station; a two-Way transducer in said additional station; and condition selector switch means in said additional station and having a first position in Which said transducer is connected to the output of said amplifier, a second position in which said transducer is connected to a set of terminals in said additional station for connection with said amplifier through switch means in said master station, and a third position in which said transducer is connected directly to the input of said amplifier and incoming calls to said additional station are blocked.

5. In an intercommunication system: a radio receiver; an amplifier having an input connected with said radio receiver and having an output; a power source connected with said radio receiver and said amplifier; a plurality of interconnected stations, each having a two-way transducer connectable with the input or the output of said amplifier for originating and receiving signals therefrom; condition selector switch means in each of said stations for establishing connections between said transducers and said amplifier, said condition selector switch means having a first position in which the transducer is connected with the input of said amplifier for originating calls, and incoming calls are blocked, a second position in which said transducer is connected with the output of said amplifier for monitoring all calls on the system, and third and fourth positions which said transducers are alternatively connected with the output and input of said amplifier for receiving and sending calls in a two-way conversation, said switch means including contacts operative only in the first and second conditions for completing the power circuit to said radio, said radio power circuit being broken when any one of said switch means is in said third or fourth position.

6. In an interconimunication system: an amplifier having an input and an output; a call-originating station hav- 9 ing a first two-Way transducer; a call-receiving station having a second two-Way transducer; station selector switch means at said call-originating station operable to effect an interconnection between said stations for twoway communication; a condition selector switch means at said call-originating station, said first transducer being selectively connectable with the input and output of said amplifier through said condition selector switch means for transmitting and receiving messages, respectively; and further condition selector switch means at said call-receiving station, having a private position in which said second transducer is connected directly with the output of said amplifier and a non-private position in which said transducer is connected with terminals for selection by a call-originating station and connected through the station selector switch means and condition selector switch means of the call-originating station with the input and output of 10 said amplifier, to conduct a two-way conversation with the call-originating station.

References Cited in the file of this patent UNITED STATES PATENTS 1,824,726 Lowell Sept. 22, 1931 2,258,807 Pitken Oct. 14, 1941 2,402,599 Charchian June 25, 1946 2,496,398 Lambert Feb. 7, 1950 2,512,834 Legerth June 27, 1950 2,671,134 Chrystie Mar. 2, 1954 2,676,206 Bennett et al Apr. 20, 1954 2,752,426 Campbell June 26, 1956 2,754,456 Madelung July 10, 1956 2,759,133 Mueller Aug. 14, 1956 2,812,393 Patrick Nov. 5, 1957 2,850,569 Flury Sept. 2, 1958 2,859,286 Kennedy Nov. 4, 1958 

1. IN AN INTERCOMMUNICATION SYSTEM: A PLURALITY OF STATIONS; AN AMPLIFIER IN SAID SYSTEM HAVING AN INPUT AND OUTPUT; A TWO-WAY TRANSDUCER IN EACH STATION; STATION SELECTOR SWITCH MEANS IN A FIRST OF SAID STATIONS CONTROLLING INTERCONNECTION OF SAID FIRST STATION WITH A SELECTED OTHER STATION; CONDITION SELECTOR SWITCH MEANS IN SAID FIRST STATION ACTUABLE TO CONTROL CONNECTION OF THE TRANSDUCERS IN SAID FIRST AND SAID SELECTED OTHER STATIONS WITH THE INPUT AND OUTPUT OF SAID AMPLIFIER TO CARRY ON A TWO-WAY CONVERSATION; A FIRST TERMINAL IN SAID OTHER STATION CONNECTED DIRECTLY WITH THE OUTPUT OF SAID AMPLIFIER; A SECOND TERMINAL IN SAID OTHER STATION CONNECTED WITH THE STATION SELECTOR SWITCH MEANS OF SAID FIRST STATION; AND SWITCH 